> On Wed, Mar 07, 2007 at 02:19:22PM +0100, Peter Zijlstra wrote: > > On Wed, 2007-03-07 at 14:08 +0100, Nick Piggin wrote: > > > > > > > The thing is, I don't think anybody who uses these things cares > > > > > about any of the 'problems' you want to fix, do they? We are > > > > > interested in dirty pages only for the correctness issue, rather > > > > > than performance. Same as reclaim. > > > > > > > > If so, we can just stick to the dead slow but correct 'scan the full > > > > vma' page_mkclean() and nobody would ever trigger it. > > > > > > Not if we restricted it to root and mlocked tmpfs. But then why > > > wouldn't you just do it with the much more efficient msync walk, > > > so that if root does want to do writeout via these things, it does > > > not blow up? > > > > This is all used on ram based filesystems right, they all have > > BDI_CAP_NO_WRITEBACK afaik, so page_mkclean will never get called > > anyway. Mlock doesn't avoid getting page_mkclean called. > > > > Those who use this on a 'real' filesystem will get hit in the face by a > > linear scanning page_mkclean(), but AFAIK nobody does this anyway. > > But somebody might do it. I just don't know why you'd want to make > this _worse_ when the msync option would work? > > > Restricting it to root for such filesystems is unwanted, that'd severely > > handicap both UML and Oracle as I understand it (are there other users > > of this feature around?) > > Why? I think they all use tmpfs backings, don't they? > > > msync() might never get called and then we're back with the old > > behaviour where we can surprise the VM with a ton of dirty pages. > > But we're root. With your patch, root *can't* do nonlinear writeback > well. Ever. With msync, at least you give them enough rope.
Restricting to root doesn't buy you much, nobody wants to be root. Restricting to mlock is similarly pointless. UML _will_ want to get swapped out if there's no activity. Restricting to tmpfs makes sense, but it's probably not what UML wants. Conclusion: there's no good solution for UML in kernel-space. Miklos - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
